Generally, there are a variety of kinds of rolling mills for rolling plate and strip, and they are classified according to the number of rolls into the two-high mill, the four-high mill and the cluster mill, but the most commonly used rolling mills are the four-high mill, the HC mill and the cluster mill and so on. For two-high type, four-high type mills, there exist many disadvantages, the main disadvantage is that: when a rolled piece passes the mill stand, since the pressing devices are located at the necks of the rolls, the rolls are caused to have larger bending deformation, and the deformations of the rolls will result in the thickness error in the cross section of the rolled piece (rolled plate and strip), thus seriously affecting the quality of the rolled piece. To solve the above problem, the method of increasing the diameter of the rolls has to be adopted, and for a four-high mill, also the method of increasing the diameter of the supporting rolls has to be adopted. However, as the diameter of the rolls increases, it is certain to cause the rolling forces to abruptly increase, and the change of the rolling forces in turn causes an increase of the bending deformation of the rolls.
The cluster mills include integral housing type mills and open type mills (as shown in FIGS. 1, 2), Japanese Patent 54-1259 discloses a cluster mill which adopts a tower-like roll system. Of course, such rolling mills all have the advantage of high rigidity, but in a cluster mill, the portions of the mill stand which contact the supporting rolls still have bending deformation under rolling forces, thus causing the flexural deformation of the working rolls and affecting the uniformity of the thickness of rolled piece as a result.
The solution to the problem of the roll's flexural deformation to reduce or eliminate the effect of the roll's flexural deformation on the thickness of rolled piece consists in the control of the shape of the clearance between the working rolls to make the flexural deformation of the working rolls not to be affected by the change of rolling forces. A Chinese Patent (application number 89101393, issuance number CN 1013250B) discloses "A rolling mill with rolls of small flexure and high rigidity". To achieve above object, according to the patent, the supporting rolls at the outmost layer of the tower-like roll system are supported on the roll supports in the form of a mufti-section beam; rolling forces acting on the working rolls are transmitted respectively to the upper and lower roll supports via the roll systems; the vertical component of the force borne by the roll supports are transmitted to the mill stand via the downward acting or upward devices or similar elements such as pads; the number of the downward acting or upward acting devices is at least two, and the positions of the downward acting or upward acting devices are in the middle region of the axis of the working roll on the roll supports. It can be seen, the solution of that patent can make the flexural deformation of the roll supports in the vertical plane substantially not to vary with the rolling forces, thus effectively reducing the thickness error in the cross-section of the rolled piece. However, for the cluster mills with a tower-like roll system, the force transmitted from the working rolls to the intermediate rolls has vertical and horizontal components, therefore the peripheral supporting rolls also bear significant horizontal component force. For the rolling mill disclosed in Chinese Patent No. 89101393, the horizontal component force causes the roll supports to have horizontal flexural deformation, thus causing the intermediate rolls as well as the working rolls to have larger flexural deformation.
As stated above, for solving the problem of flexural deformation of the working rolls of a cluster mill, it is not only necessary to reduce the flexural deformation produced by the vertical component force, but also that produced by the horizontal component force, that is, it is obliged to solve the problem of deformation in two-dimensional directions, so that a working roll can be held straight and the thickness precision in the cross-section of the rolled piece is increased.